This invention relates to a method for detecting a trouble location of breakage, short circuit or the like in wire harnesses in an automotive vehicle, and to a wire harness to be used in the method.
Wire harnesses mounted in an automotive vehicle are subject to breakage or short circuit, for long time use of a car, due to interference with other parts caused by vibration during driving, wear of electric wires caused by mutual rubbing or deterioration of the wires caused by repeated bending upon opening and closing a door. When such troubles occur, electrical equipment will not operate. Heretofore, detection and repair of troubles in wire harnesses have been done by the following steps of:
(1) finding a trouble wire (circuit) by using a tester;
(2) searching electric wires arranged in an interior of an automotive vehicle by referring to a wiring circuit diagram and detaching all parts of the searched electric wire from the interior;
(3) extracting a wire harness secured to a car body by clamps or the like;
(4) detaching an exterior of the wire harness, and finding and repairing a faulty electric wire, for example, in the case of breakage of the wire, pressing a terminal onto the faulty portion, soldering it and insulating the connected portion with tape;
(5) returning the exterior of the wire harness to the original location, securing the wire harness to the car body by the clamps or the like and attaching all of the detached interior parts to the interior
In such a common process, the step (1) cannot detect a faulty location, although it can find the trouble wire (breakage or short circuit) and the steps (2) to (5) involve a considerable amount of labor and time to find the broken portion.
Heretofore, in order to overcome such a problem, for example, Japanese Utility Model Public Disclosure No. HEI 4-22311 (1992) discloses an apparatus for detecting a broken location, in which a sensing electric wire is provided close to a conductive line in electric wires for electrical wiring, the sensing wire for breakage is connected to a first terminal of an adapter, each of the conductive lines is connected to a second, third . . . terminals, and a detector including first and second measuring units, an AC power source, and an amperemeter is provided. In this apparatus, the first and second measuring units are connected to the first terminal and to a terminal corresponding to the conductive line in breakage, and an AC voltage is applied across the measuring units. A distance from a reference point to a breakage point is determined by a current value flowing between the measuring units.
The apparatus disclosed in the Public Disclosure mentioned above detects the breakage location by means of a so-called capacitance measurement method and can make it easier than the common detecting method to detect the breakage location. However, since the sensing lines must be arranged to come into close contact with the conductive wires being measured, in the case of applying them to existing wire harnesses on an automotive vehicle, it is necessary to change the type of electric wire and to increase the number of wires. This results in a large wire harness. Consequently, there are several problems that it is difficult to define an arrangement space in the automotive vehicle, interference between ambient parts and the wire harness tends to be caused, and exterior parts for protecting the wire harness will be increased. Also, this apparatus cannot detect short circuit in the wire harness and can detect only breakage.
In an underground electric cable or the like, a pulse radar method mentioned after in detail has been known to detect breakage and short circuit. However, this method has been applied to an underground electric cable which is long and has no branch. It has been difficult heretofore to directly apply the method to a wire harness which is arranged in an automotive vehicle, is short and has branches on intermedium portions.